The present invention relates to a memory device. More particularly, the present invention relates to a semiconductor device having a recess channel region including a vertical Silicon-on-Insulator (“SOI”) channel structure and a method for fabricating the same.
When a channel length of a cell transistor is decreased, ion concentration of a cell channel region is generally increased in order to maintain the threshold voltage of the cell transistor. An electric field in source/drain regions of the cell transistor is enhanced to increase leakage current. This results in degradation of the refresh characteristics of a DRAM structure. Therefore, there is a need for semiconductor devices in which the refresh characteristics are improved.
FIG. 1 is a simplified layout of a semiconductor device. The semiconductor device includes an active region 101 and a gate region 103. The active region is defined by a device isolation structure 130.
FIGS. 2a through 2c are simplified cross-sectional views illustrating a method for fabricating a semiconductor device, wherein FIGS. 2a through 2c are cross-sectional views taken along the line I-I′ of FIG. 1. A semiconductor substrate 210 having a pad insulating film (not shown) is etched using a device isolation mask (not shown) to form a trench (not shown) defining a fin-type active region 220. An insulating film for device isolation (not shown) is formed to fill the trench. The insulating film for device isolation is polished until the pad insulating film is exposed to form a device isolation structure 230. The pad insulating film is removed to expose the top surface of the fin-type active region 220.
Referring to FIG. 2b, a predetermined thickness of the device isolation structure 230 is etched using a recess gate mask (not shown) defining a gate region 103 shown in FIG. 1 to protrude an upper part of the fin-type active region 220 over the device isolation structure 230.
Referring to FIG. 2c, a gate insulating film 260 is formed over the protruded fin-type active region 220. A gate structure 295 is formed over the gate insulating film 260 of the gate region 103 shown in FIG. 1 to fill the protruded fin-type active region 220, wherein the gate structure 295 comprises a stacked structure of a gate electrode 265 and a gate hard mask layer pattern 290.
FIG. 3 is a simplified cross-sectional view illustrating a semiconductor device. If a voltage above the threshold voltage is applied to the gate, an inversion layer IL and a depletion region DR are formed in a semiconductor substrate under the gate insulating film 360.
According to the above conventional method for fabricating a semiconductor device, device characteristics such as the gate potential and ion concentration of a cell channel structure have to be adjusted in order to secure a desired Off-characteristic of the device, which causes increased leakage current from a storage node to the body of the semiconductor substrate. Accordingly, it is difficult to obtain proper refresh characteristics of the device due to the increased leakage current.